Distribution of Ostreid herpesvirus-1 (OsHV-1) microvariant in seawater in a recirculating aquaculture system

Ostreid herpesvirus-1 (OsHV-1) microvariant presents a significant threat to the commercial production of Crassostrea gigas worldwide. Investigating the transmission of the virus in the estuarine environment where oysters are grown has proven to be difficult due to the complexity of the ecosystem. The aims of this trial were to (1) investigate the distribution of OsHV-1 in seawater over time in a recirculation system during an experimental disease outbreak; (2) assess the effects of the biofiltration and ultraviolet light components of the recirculation system on the detection of OsHV-1; and (3) assess the potential for OsHV-1 to associate with particles in the artificial seawater matrix. The source of virus was experimentally infected donor and cohabitating recipient oysters. Both the presence of infected oysters and the biofilter and UV light source significantly affected the detection rate of OsHV-1 in seawater. It was detected more frequently after high dose exposure (n=6 donors per tank) compared with low dose exposure (n=2 donors per tank), and when the biofilter and UV were disconnected from the treatment tanks. The odds of detecting OsHV-1 in the treatment tanks, which were periodically disconnected from the biofilter and UV, were 2.56 that of the system sumps which were always connected to the biofilter and UV. It may not be possible to remove OsHV-1 completely from the seawater of a recirculation system during a disease event using biofiltration and UV irradiation alone. The presence of food did not significantly affect the detection rate of OsHV-1 in seawater. The pellet produced by low speed centrifugation of seawater had similar to 2 to 5 fold greater odds of being positive for OsHV-1 by qPCR, in comparison to unprocessed seawater and the supernatant fraction. These results are consistent with the hypothesis that OsHV-1 may be attached to particles, which in this model may include algal feed, oyster faeces, fragments of oyster tissues or microorganisms introduced to the system with the oysters, but confirmation of this is required. (C) 2016 Elsevier B.V. All rights reserved.